1. Field
The invention relates to wired communication systems and specifically to controlling the impedance of an electrical signal interface of a network.
2. Background
Consider several communication nodes that are part of the same coaxial cable network or other wired network. Each node connecting to the network presents an impedance at the point of connection. Mismatches between the impedance of the node and the impedance looking into the network cause reflections. Such reflections cause a multipath signal environment that impairs passage of the signal over the medium. The input and output of the nodes include active circuitry that changes its impedance when power is applied and removed. The impedance can also change when other events occur. For example, a reset of a node can temporarily deactivate circuitry. If the nature of the reflections is known, compensation can be provided. However, as the reflections change, the compensation must change also. Adaptation to such changes takes time to complete. Sub-optimal compensation of the changed environment can cause degradation in the performance of the network, including a reduction in link margins and an increase in the data error rate.
Accordingly, it is desirable to ensure that the communication channel and other operational nodes of the network are not disturbed when power is applied to, or removed from one or more nodes or when another event changes the impedance that the node presents to the network.